The 3rd Generation Partnership Project (3GPP) sets standards and technical specifications for a 3G mobile system referred to as Long Term Evolution (LTE). The LTE system includes an Evolved Packet System (EPS) with a main component called Evolved Packet Core (EPC). EPC comprises three main subcomponents: a Mobility Management Entity (MME), a serving gateway (SGW), and a packet data network gateway (PDN-GW). The 3GPP published “LTE; General Packet Radio Service (GPRS) enhancements for Evolved Universal Terrestrial Radio Access network (E-UTRAN) access,” TS 23.401 Version 9.5.0 Release 9, defining the EPS service description.
In LTE, a user equipment (UE) device, such as a mobile phone, communicates with a SGW which in turn communicates with a PDN-GW. The PDN-GW communicates further with an internet protocol (IP) service such as an IP multimedia subsystem (IMS), voice over IP (VoIP), and mobile broadband. The operator's IP services are provided over an IP-PDN that is identified by a UE device with an access point name (APN). The series of communications between an APN and a UE device provide data connectivity to UE devices in the LTE mobile system and is referred to as a PDN connection. Thus, in each PDN connection, the PDN-GW couples an SGW with the APN and the SGW couples the UE device with the PDN-GW. In this scenario, each PDN connection (also referred to as a UE session) has corresponding PDN connection information (also referred to as UE session information).
However, 3GPP's specification of LTE does not address some of the mission critical aspects of EPC. For example, the specification does not address geographic redundancy, where one or more PDN-GWs or SGWs may be lost. Nor does the specification address in-service maintenance, where any PDN-GW or SGW must be brought out of service for maintenance.
Given that EPS targets full migration of voice services to IP-PDNs, operators are becoming more and more concerned with redundancy scenarios. 1+1 network level solutions exist, but such solutions are unnecessarily costly, since 50% of the available processing and forwarding capacity is used only for redundancy.